In the field of graphic arts, an image forming system showing superhard tone photographic characteristics is required for improving the reproduction of images having continuous gradation with halftone images or the reproduction of line drawing images.
For such a purpose, a special developing solution called a litho-developing solution has been used hitherto. The litho-developing solution contains only hydroquinone as a developing agent, wherein sulfite, which is a preservative, is used in a state of an adduct of formaldehyde so as not to hinder infectious developability of the developing agent and the concentration of free sulfite ion is very low. Therefore, the litho-developing solution has a serious disadvantage in that it cannot be preserved over 3 days, because it is easily subject to air oxidation.
As a process of obtaining superhard tone photographic characteristics with a stabilized developing solution, there is a process using hydrazine derivatives described in U.S. Pat. Nos. 4,224,401, 4,168,977, 4,166,742, 4,311.781, 4,272,606, 4,221,857 and 4,243,739. According to this process, superhard tone photographic characteristics are obtained in high sensitivity. Further, since it is possible to add a high concentration of sulfite to the developing solution, the stability of the developing solution to air oxidation is remarkably improved as compared with the litho-developing solution.
U.S. Pat. No. 4,269,929 has disclosed a process of hard tone development which comprises bringing a photographic element having at least a silver halide emulsion layer in contact with an alkali developing solution having a pH value of 10 to 12 which contains a dihydroxybenzene developing agent, a 3-pyrazolidone developing agent, a sulfite preservative and an amino compound in an amount for accelerating contrast, in the presence of hydrazine derivatives. It has been described that, according to this process of hard tone development, the amino compound employed in an amount for accelerating contrast not only maintains hard tone characteristics but also can improve the stability of the developing solution to air oxidation because the hard tone development characteristics are obtained even if the pH of the developing solution is reduced. It has been described in the Examples thereof that such effects are obtained with 3-diethylamino-1-propanol, 2-methylamino-1-ethanol, 2-diethylamino-2-ethanol, diisopropylamine, 5-amino-1-pentanol and 6-amino-1-hexanol, etc.
However, since such amino compounds are used in an amount of 10 g to 200 g per liter of the developing solution, there are problems that the chemical cost of the developing solution becomes high and dissolution of the silver halide occurs due to the presence of a large amount of the amino compound.
The fact that the amino compound in the developing solution dissolves silver halide has been described in C. E. K. Mees, The Theory of the Photographic Process, 3rd Edition, page 370, and L. F. A. Mason, Photographic Processing Chemistry, page 43. Thus, it is not desirable to employ a large amount of a compound which dissolves silver halide in the developing solution. For example, in a process which comprises developing a silver halide photographic light-sensitive material by an automatic developing apparatus, wherein a supplementary liquid is supplied to a development tank according to the area of the film, as is conventionally used in this field of the art, if the developing solution as described above is used for a long period of time, a phenomenon that silver halide eluted from the film adheres as silver to the wall of the tank in the automatic developing apparatus or rollers conveying the film occurs. The silver adhering to the rollers is transferred to the film to cause silver stain on the films, whereby the quality of image is remarkably reduced. The silver stain is formed on both of the high density part having a large rate of dot area and the low density part having a low rate of dot area, but silver stain on the low density part is particularly visually conspicuous.